1. Field of the Invention
The present invention relates to a light source, and especially to a light source used in a backlight module for a device such as a liquid crystal display.
2. General Background
Liquid crystal displays are commonly used as the display device for compact electronic apparatuses, because they not only display good quality images with little power but also are very thin. However, the liquid crystals in a liquid crystal display do not emit any light themselves. The liquid crystals have to be lit up by a light source so as to clearly and sharply display text and images. Typically, light emitting diodes (LED) are used as light sources because of their high luminance and low loss.
A typical backlight module 40 as shown of FIG. 4 includes a light guide plate 400. The light guide plate 400 has a surface 420 functioning as a light incident surface, and a surface 440 opposite to the light incident surface 420 functioning as a light emitting surface. A plurality of cold cathode fluorescent lamps (CCFLs) 422 are arranged parallel to each other on a substrate 410 so that they are opposite to the light incident surface 420. Light beams from the light source 422 enter the light guide plate 400 through the light incident surface 420, and finally emit out from the light guide plate 400 through the light emitting surface 440.
However, the high voltage and high current intensity of the CCFLs 422 lead to heavy power consumption, especially in notebook computer applications. In contrast, an LED light source has the advantage of low voltage and low current intensity, which provide low power consumption. Thus, replacing a CCFL light source with an LED light source can save a lot of power.
FIG. 5 is a schematic, side cross-sectional view of a conventional light source 50. The light source 50 includes a plurality of LED groups 520 arranged on a substrate 500.
FIG. 6 is a top plan view of the light source 50. Each LED group 520 includes three LEDs: a red LED 520A, a green LED 520B, and a blue LED 520C, which are arranged in a particular configuration relative to each other. Since all colors can originate from the three primary colors red, green and blue, each primary color LED 520A/B/C can emit from 32 to 256 gray levels. Thus, the combination of three primary color LEDs 520A/B/C can achieve from 32,768 to 16×106 gray levels. The light source 50 has the advantage of low power consumption, and different colors can be achieved by controlling respective outputs of the primary color LEDs 520A/B/C.
However, the LED light source 50 generally requires a large number of the primary color LEDs 520A/B/C. In addition, and the arrangement of the primary color LEDs 520A/B/C is fixed, and manufacturing of the fixed arrangement of the primary color LEDs 520A/B/C can be problematic.
What is needed, therefore, is a backlight module and a light source used therein which are relatively inexpensive.